Wednesday, December 23, 2015

Australia: Caves and Crustaceans

Tasmanian Mountain Shrimp ( Anaspides tasmaniae)
Tasmania has its own array of special plants and animals - some in their last refuge after disappearing from the Australian mainland in the comparatively recent past, others long isolated on the island. Of all of them, though, the one I most wanted to find - short of having a Thylacine (Thylacinus cyanocephalus), the now-extinct marsupial 'wolf', rise from the dead and cross the road in front of us - was an obscure, and not terribly exciting-looking, crustacean, only about five centimetres long. Meet the Tasmanian Mountain Shrimp ( Anaspides tasmaniae).

We were now (March 26, 2014) on our way from Launceston, where we had spent the last two nights, driving westward over the highlands.  Our goal was Cradle Mountain, Tasmania's most famous natural beauty spot. About halfway along, just past the town of Mole Creek, the road passes a series of splendid caves.  I confess I am a tad claustrophobic about visiting caves, but I couldn't pass up giving Ryan the opportunity (even though Sarawak, Ryan's home, has some pretty spectacular caves of its own).

The two main cave systems, Marakoopa and King Solomon's Cave, are part of the Mole Creek Karst National Park, and to get in you need tickets (you can see them in my hand).  We did not have time for both, so I decided to take Ryan on one of the tours of Marakoopa Cave.  It not only promised some spectacular geology, but the largest publicly-accessible glow-worm display in Australia.  We saw our first Mountain Shrimp on the way in - but let's save that for later.

First, the cave itself.  'Marakoopa' means 'handsome', and an appropriate name it is, too.  Carved out of Ordovician limestone, the cave system contains a number of magnificent chambers.  Because it is a so-called 'wet' cave, with two underground streams running through it, it is also a rich habitat for cave life.

Our guide led us into the recesses of the cave...

... where we were treated to clusters of spectacular formations, including curtains of fine, threadlike stalactites hanging over cone-shaped stalagmites rising from the cave floor.

A series of staircases took us from one chamber to another.

The largest chamber has been named "The Cathedral', and it's not difficult to see why.  Ryan liked it.

The walls were decorated with tassel-like hangings, looking more like strands of melted wax than the massive stalactites of other caves.

Tasmanian Glow-worm (Arachnocampa tasmaniensis)
Tasmanian Glow-worm (Arachnocampa tasmaniensis)
From the ceiling hung the natural lighting of the cave: the strands of the Tasmanian Glow-worm (Arachnocampa tasmaniensis).  Arachnocampa is a genus of fungus gnats (Keroplatidae) confined to caves in eastern Australia and New Zealand (where the hanging strands of A. luminosa are a common and widespread tourist attraction; Eileen and I toured the famous Waitomo Glow-worm Caves in 2011).  The glow is produced by larval gnats that live in mucus tubes on the cave roof; the suspended strands are actually snares studded with adhesive mucus, there to trap flying insects that blunder into them.

Tasmanian cave spider (Hickmania troglodytes)
The other well-known inhabitant of Marakoopa Cave is the Tasmanian Cave Spider (Hickmania troglodytes).  Like the Mountain Shrimp, this is a unique creature, found only in Tasmania, where large numbers can be found around the mouths of caves.  It is apparently of ancient lineage; its only near relatives, the other eight members of the family Austrochilidae (missing-link spiders), live in the Andean forests of South America, making Hickmania a probable relic of the ancient southern continent of Gondwanaland.  Austrochilids earn their name by being a sort of link (non-missing, of course) between the two main lineages of spiders today, the mygalomorphs (such as tarantulas) and the araneomorphs (pretty much everything else). What is more, Cave Spiders may live for several decades. 

Tasmanian cave spider (Hickmania troglodytes)
Our guide took care to show us this one, a female is guarding her egg-case, a peculiar object in itself.  According to the Australian Museum web page on the species, "Within the thick, white outer silk walls, the eggs lie enclosed in a rigid, thimble-like structure, which is suspended so that it doesn't touch the outer wall. This 'thermos-like' structure may buffer the eggs against climatic changes and contaminants - the silk also seems very resistant to attack by fungi and bacteria. The female guards her egg sacs, and females living outside caves usually disguise their sacs with fragments of wet, rotting wood. Spiderlings emerge from the sacs after eight to ten months, an unusually long time, and disperse within a month."

The entrance to the cave follows one of Marakoopa's two streams, and it was here - both as we entered and left - that we found the Mountain Shrimp.  It is not really a cave animal (though it has relatives in Tasmania that are), but the stream just past the entrance proved to be an excellent place to find one.

Tasmanian Mountain Shrimp ( Anaspides tasmaniae)
So what is so exciting about this rather unprepossessing animal?  Well, for one thing, it is of extremely ancient lineage.  Very similar creatures were around in the Carboniferous, 300 to 360 million years ago.  The group of crustaceans to which it belongs, the Syncarida, was in fact first described from marine fossils, well before living examples turned up (the first in a well in Prague in 1882; the Tasmanian Mountain Shrimp was officially described in 1893).  Most of the 250 or so living syncarids are tiny creatures, living in caves or groundwater in many parts of the world.  Though it has more distant relatives in South America, New Zealand and southeastern Australia, the family to which the Mountain Shrimp belongs, the Anaspididae, is found only in Tasmania.  There are only four other species, all much harder to find.

Tasmanian Mountain Shrimp ( Anaspides tasmaniae)
The Mountain Shrimp, to sum up, is a true living fossil - a glimpse into the unfathomably distant past.  Perhaps the most noticeable thing about it is that it lacks a carapace, the hard, fused shell that covers the front part of the body in more advanced crustaceans such as lobsters, crabs and "true" shrimp.  While elsewhere in the world its relatives have retreated to the depths of caves, wells and aquifers, in Tasmania the Mountain Shrimp continues to live in the open.  It spends its days puttering about in alpine waters in search of anything from bits of moss to carrion to tiny worms.  It, and its ancestors, have probably been doing much the same for over three hundred million years.  I counted myself privileged indeed to have met it.

Orange-legged swift spider (Nyssus coloripes)
Out of the cave, and past the stream with its ancient shrimp, we were back in the world of more ordinary creatures - though, of course, with their own peculiarities.  The Orange-legged Swift Spider (Nyssus coloripes), a species found throughout Australia, is, apparently, a wasp mimic.  This spider is a member of the family Corinnidae, and a good many corinnids are mimics of either ants or wasps - presumably to convince predators that they are not worth eating (ants, whose bodies are filled with formic acid, are avoided by many insect-eaters) or that they might pack a powerful sting (several of them mimic the flightless female wasps known as "velvet ants", creatures well worth avoiding).  In both colour and actions, this species resembles females of certain ground-crawling, spider-hunting wasps, and, it seems, benefits accordingly. 

 I found this colourful fly sitting on a fern frond.  I have no idea what sort of fly it is (a tabanid, perhaps?).

Black Currawong (Strepera fuliginosa)
Black Currawong (Strepera fuliginosa)
Finally, before we met Eileen and got back in the car to continue our journey, I took a last stop to photograph a Black Currawong (Strepera fuliginosa)- not a living fossil, or a Gondwanan relic, but nonetheless a species that you can only see in Tasmania.  You just don't have to explore a cave to do it.

1 comment:

  1. What spectacular caves! Cave life fascinates me.. many of the animals live in constant darkness and one wouldn't expect to find such a diversity of life there, yet, there are such localised and specialised species living. The shrimp is amazing. The lack of a carapace makes it look prehistoric immediately. Great find!